While the Met Lab
labored to make headway on pile (reactor)
design, Glenn T.
Seaborg (right) and his coworkers were trying to learn enough about
transuranium chemistry to ensure that plutonium
could be chemically
separated from the uranium
that would be irradiated in a production pile. Using lanthanum
fluoride as a carrier, Seaborg isolated a weighable sample of plutonium in
August 1942. At the same time, Isadore Perlman and William J. Knox
explored the peroxide method of separation; John E. Willard studied various
materials to determine which best adsorbed (gathered on its surface)
plutonium; Theodore T. Magel and Daniel K. Koshland, Jr., researched
solvent-extraction processes; and Harrison S. Brown and Orville F. Hill
performed experiments into volatility reactions. Basic research on
plutonium's chemistry continued as did work on radiation and fission
products.

Seaborg's
discovery and subsequent isolation of plutonium were major events in the
history of chemistry, but it remained to be seen whether they could be
translated into a production process useful to the bomb effort. The
laboratory process created by Seaborg would have to be scaled-up a billion-fold
to be implemented in an industrial separation plant.

Collaboration with DuPont's Charles M. Cooper and his staff on plutonium
separation facilities began even before Seaborg succeeded in isolating a
sample of plutonium. Seaborg was reluctant to drop any of the
approaches then under consideration, and Cooper agreed. The two
decided to pursue all four methods of plutonium separation but put first
priority on the lanthanum fluoride process Seaborg had already
developed. Cooper's staff ran into problems with the lanthanum
fluoride method in late 1942, but by then Seaborg had become interested in phosphate
carriers. Work led by Stanley G. Thompson found that bismuth
phosphate retained over ninety-eight percent plutonium in a
precipitate. With bismuth phosphate as a backup for lanthanum
fluoride, Cooper moved ahead to create an experimental production facility
near Stagg Field.

By
late 1942, experiments with the lanthanum fluoride process in Chicago had
gone well enough that DuPont moved into the plant design stage and
converted the facility at the Met Lab to experiment with the use of bismuth
phosphate. In late May 1943, DuPont pushed for a
final decision on which of the two processes to use. Greenewalt chose
bismuth phosphate (right), even though Seaborg admitted he could find
little to distinguish between the two. Greenewalt based his decision
on the corrosiveness of lanthanum fluoride and on Seaborg's guarantee that
he could extract at least fifty percent of the plutonium using bismuth
phosphate. DuPont began constructing the chemical separation pilot
plant at Oak Ridge,
while Seaborg continued refining the bismuth phosphate method.

It was now Cooper's job to design the new experimental production
pile as well as the plutonium extraction facilities at Oak Ridge,
both complicated engineering tasks made even more difficult by high levels
of radiation produced by the process. Not only did Cooper have to
oversee the design and fabrication of parts for yet another new Manhattan
Project technology, he had to do so with an eye toward planning the Hanford facility. Radiation safety
was a major consideration because of the hazards of working with plutonium,
which was highly radioactive. Uranium, a much less active element
than plutonium, posed far fewer safety problems.